1. Field of the Invention
The invention relates to a method of spin-welding a moulded plastics end component into an open end of an extruded plastics tube.
Spin-welding is a well known technique for welding together plastics components which are assembled with opposed annular surfaces, in which one of the components is spun at high speed relative to the other to cause welding and subsequent fusion of the plastics material at the interface of the opposed surfaces.
It has been found in the past that a certain radial pressure is necessary at the welding interface to generate the heat required for melting of the plastics material. This radial pressure has been provided in the past by an interference fit between the components and by external supporting means which restrain radial expansion of the components during assembly and subsequent spin welding. One of the drawbacks of spin-welding has been the fact that very fluid liquid plastics material--"flash"--can often escape from the weld area and may solidify as unsightly debris.
2. Prior Art
U.S. Pat. No 3,982,980 describes a method of making a cartridge for dispensing materials. A resin tube is extruded to have constant inside and outside diameters and the tube is cut off in equal lengths to provide the barrels of the cartridges and having ends evenly severed in planes perpendicular to the longitudinal axes of the barrels. Injection moulded end caps are fitted into the cut ends of the barrels with an interference fit and are then spin welded. During the assembly and spin welding process, the barrels are restrained against radial expansion by a surrounding tool which rotates with the end cap and is provided with cutting surfaces for the removal of flash debris.
There are several disadvantages associated with this prior method. First, the provision of an external restraint inevitably leads to marking of the external surface of the tube. Second, the plastics components and the surrounding tool must be manufactured within strict tolerances if reliable welds are to be produced. In this respect, the extrusion and cooling of the tubing must be controlled to keep the tubing accurately to the desired internal and external diameters. A third disadvantage arises from the configuration of the end cap which is of a countersunk design and has a tendency to dome outwardly when the container is pressurised, thus subjecting the weld to peel stresses which are likely to cause failure.